This invention relates to an exposure slit apparatus for use in an optical system of a reproducing machine preferably of the electrostatographic type. The machine preferably includes means for copying documents selectively at one of a plurality of magnifications.
In an optical system for stripwise viewing a document the projected illumination intensity tends to fall off at the edges of the image as compared to the center thereof. To compensate for this problem exposure slits have been employed which allow a greater portion of the projected image rays to pass through the slit at edges of the image than in the middle thereof. It has been common practice to employ such a slit either directly above the imaging surface or at a position nearer the object plane.
In at least one machine the Xerox 840 machine two exposure slits are utilized, one near the object plane and the other near the image plane or xerographic drum. In machines such as the Xerox 840 which provide a plurality of projected image magnifications further complications occur since it is necessary to compensate not only for the normal fall off in illumination toward the edges of the image, but also for the changes in illumination resulting from the magnification changes. U.S. Pat. No. 3,917,393 to Nier is exemplary of designs for an exposure slit system which are capable of compensating for magnification change as well as illumination fall off.
The machine which will be described hereafter utilizes two illumination slits, one positioned near the object plane and the other adjacent the image plane or xerographic drum. The object plane slit controls illumination during a reduction mode of copying whereas the image plane slit controls illumination during normal 1:1 or base mode of copying.
A difficulty which arises when one attempts to incorporate multiple exposure slits in a highly compact reproducing machine is the inability to appropriately locate or mount the exposure slits within the space available. In accordance with this invention the space constraints have been overcome by a unique arrangement wherein a reflector in the optical system is configured with a reflecting surface whose boundaries conform to a desired exposure slit profile.
A variety of electrostatographic reproducing machines are commercially employed which have different modes of operation. One type of machine utilizes a moving original exposure system wherein an original document is moved past a fixed slit optical system for projecting an image onto the moving photoconductive surface. These machines include a means for changing the magnification of the projected image to provide reduction copies. Exemplary of patents in this area is U.S. Pat. Nos. 3,076,392, to Cerasani et al., and 3,649,114 to Vlach et al.
Other machines have been adapted to copy stationary original documents at a variety of magnifications or reductions through the use of a scanning optical system. Exemplary of patents in this area are U.S. Pat. Nos. 3,476,478, to Rees, Jr.; 3,542,467 to Furgeson; 3,614,222 to Post; and 3,837,743 to Amemiya. Another approach which has been utilized for projecting images for reproduction at varying magnifications from a stationary original comprises full frame exposure. Exemplary of patents in this area are U.S. Pat. Nos. 3,543,289 to Koizumi; 3,687,544 to Muller; 3,703,334 to Knechtel; and German Offenlegungsschrift No. 2,154,944 to Libby.
U.S. Pat. Nos. 3,703,334 to Knechtel and 3,837,743 to Amemiya set forth above are also singificant in that they disclose the use of a separate reflector or add reflectors, respectively, which are selectively positionable in the optical path for changing the conjugate distance of the optical system for providing varying magnifications.
The aforenoted machines are adapted to provide one or more modes of copying having different magnifications. In the optical systems of these machines, some means is usually provided for changing the conjugate relationship of the object and image sides of the projection lens. This may be accomplished by translating the lens between different positions for different projected image magnifications or in accordance with an alternative approach by utilizing more than one lens whereby different lenses are selectively positionable in the optical path, depending upon the projected image magnification desired. See, for example, U.S. Pat. No. 3,779,642 to Ogawa.
Other forms of multi-mode copiers are available commercially. For example, in the Xerox 3100 LDC machine an optical system is provided which enables the machine to copy from a stationary original in a first scanning mode or from a moving original in a second fixed optical mode. This latter mode is particularly adapted for copying documents larger than the conventional viewing platen size. U.S. Pat. No. 3,900,258 to Hoppner et al. [1] is illustrative of a machine similar in many respects to the 3100 LDC machine.
Reproducing apparatuses including the capability of making copies from both moving and stationary originals are also described in U.S. Pat. No. 3,833,296 to Vola, and in IBM Technical Disclosure Bulletin, Vol. 12, No. 1, at page 173, June 1969.
It has been found desirable, to provide a multimode reproducing apparatus having various unique features of the 3100 LDC machine, including its extremely compact size, but also having the capability of reduction copying.
One approach to such a machine is described in U.S. application Ser. No. 588,971, filed June 20, 1975, now U.S. Pat. No. 4,027,963, to Hoppner et al. [2]. In that application a multi-mode reproducing apparatus is provided including both moving and stationary original exposure modes, with at least two modes of moving original exposure at differing copy image magnifications. The Hoppner et al. [2] machine includes a first optical mode wherein a stationary document is viewed and an image thereof is projected onto a moving imaging surface. In a second mode a document moving at a first speed synchronized to the speed of the moving imaging surface is viewed and an image thereof projected onto the imaging surface at a desired magnification. In a third mode a document moving at a second speed synchronized to the speed of the moving imaging surface is viewed and an image thereof projected onto the surface at a reduced magnification. In the reduction mode of operation a scanning optical system is held fixed at a given position and an additional optical element comprising an add mirror is inserted into the optical path in order to change the conjugate on the object side of the lens. The lens is also shifted to a new position to align it with a repositioned optical path.